Screening of Some Citrus Genotypes for Salinity Tolerance Using Physiochemical Methods

Large samples of citrus genotypes need to be evaluated to find and improve the genetic resources for producing better hybrid rootstocks. Two well-known tolerant (‘Cleopatra’ mandarin) and sensitive (‘Troyer’ citrange) cultivars, and 10 genetically diverse citrus genotypes from Iran were examined under four sodium chloride (NaCl) levels, including 0, 2, 4, and 6 dS m⁻¹, to screen and discover salt-tolerant genotypes. Salinity (especially at 6 dS m⁻¹) had a detrimental effect on plants by reducing relative water content (RWC; −27.34%), water potential (−220%), total chlorophyll content (−61.97%), and enhancing Na⁺ (500%), Cl⁻ (136%) concentration, as well as cell oxidative level (electrolyte leakage [EL; 61.92%], malondialdehyde [MDA; 64.05%]). In reaction to salinity, osmoprotectant content (soluble sugars [163%] and proline [101%]) and antioxidant enzymes activity (superoxide dismutase [SOD; 336%], catalase [CAT; 53.54%], peroxidase [POD; 77.06%], and ascorbate peroxidase [APX; 421%]) increased dramatically especially at 6 dS m⁻¹. In addition, under different salinity levels, genotypes exhibited different responses, but ‘Cleopatra’ mandarin and G5 exhibited the highest RWC, water potential, chlorophylls, soluble sugars, proline, and antioxidant enzymes activity, as well as the lowest Na⁺, Cl⁻ concentrations, EL, and MDA. Overall, G5 was identified as the genotype with the highest salt tolerance and can be used in gardens that have salt stress problems.